Tree rings from oak and pine across northwest Europe have remained undatable for decades, but a new project will use chemical signatures locked inside the wood to assign them to specific calendar years for the first time. The problem is that standard tree-ring dating relies on measuring ring widths, which only works well when trees grow under environmental stress—at high altitudes or latitudes. In regions like northwest Europe, where climate rarely limits growth, the rings are too uniform to match against known chronologies. This leaves thousands of archaeological timbers and artefacts without precise dates, and prevents scientists from reconstructing past summer climate for densely populated, historically rich areas. The QUERCUS project will build the first annually-resolved isotopic chronologies for northwest Europe spanning roughly 4,500 years, back to the Bronze Age. By measuring stable isotopes of carbon and oxygen within each ring, the team can extract strong climate signals even from trees that grew in benign conditions. If successful, the method will date previously undateable wood, and deliver quantified reconstructions of summer climate for regions where climatic shifts have shaped human societies over millennia. This is fundamental science—it will not directly change infrastructure or daily life, but it will provide a precise chronological backbone for archaeology and climate science across a vast, culturally important region.
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Dendrochronology, or tree-ring dating, is the most precise dating method in science-based archaeology. It allows the growth of an individual tree ring to be assigned to a single calendar year and, where wood samples retain the bark-edge, it is possible to determine the season and the year in which the tree died, or was felled. The method can provide absolute calendar dates and has revolutionised the dating of wooden structures and artefacts across Europe. Where the trees grew under strong environmental stress, typically at high altitude or latitude, it is also possible to extract information on the climate of the past. However, dendrochronology and dendroclimatology are constrained by the length and variability of the tree-ring sequence being dated, as well as by the tree species, age and provenance. This means that a large proportion of samples, particularly those from regions such as NW Europe where climate rarely limits growth, cannot be dated or used for historical climate reconstruction. Using stable isotopes rather than ring widths, for both dating and palaeoenvironmental reconstruction, the QUERCUS project will develop the first annually-resolved isotopic chronologies for NW Europe extending c. 4,500 years to the Bronze Age. QUERCUS will advance the technique for species and regions where chronology and palaeoclimate data are most needed, to permit short sequence, inter-genus and multi-method dating of archives and artefacts that have remained undateable since the development of scientific dendrochronology. The stable isotope chronologies carry strong climate signals, and can be used to reconstruct the climate of the past even when the trees were not growing under environmental stress. Using a multi-disciplinary approach, these records, calibrated using some of the longest instrumental series in the world, will deliver unrivalled quantified reconstructions of summer climate for culturally-rich, populous regions where climatic change has impacted upon society over millennia.
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